1. Field of the Invention
This invention generally relates to a bicycle rear derailleur. More specifically, the present invention relates to a B-axle of a bicycle rear derailleur.
2. Background Information
Bicycling is becoming an increasingly more popular form of recreation as well as a means of transportation. Moreover, bicycling has become a very popular competitive sport for both amateurs and professionals. Whether the bicycle is used for recreation, transportation or competition, the bicycle industry is constantly improving the various components of the bicycle. One component that has been extensively redesigned is the bicycle rear derailleur.
Typically, a rear derailleur has a base member and a movable member with a chain guide movably coupled to the base member via a linkage assembly. The base member is typically coupled to the rear triangle of the bicycle frame by a bolt that forms a B-axle for providing limited rotation with respect to the bicycle frame. The chain guide is configured to move the chain laterally over a plurality of rear sprockets. The chain guide is typically coupled to the movable member by a shaft that forms a P-axle for providing limited rotation of the chain guide with respect to the movable member. The linkage assembly typically includes a pair of pivotal links pivotally coupled to both the base member and the movable member using pivot pins. A spring typically biases the chain guide to an innermost or outermost position relative to the rear sprockets. A bowden-type control cable with an outer sheath and an inner wire is typically coupled between the rear derailleur and a conventional shift control device. Thus, the chain guide can be moved laterally by moving the linkage assembly via the inner wire. Pulling the inner wire moves the chain guide against the biasing force of the spring, while releasing the inner wire causes the chain guide to move due to the biasing force of the spring.
Two examples of rear derailleurs are disclosed U.S. Pat. No. 4,469,479 and U.S. Patent Publication No. 2006/0105869. While these rear derailleurs usually work well, it is desirable to make the rear derailleur as light as possible without sacrificing strength. Typically, rear derailleurs use a steel bolt as the B-axle, which is a relatively heavy material. To reduce the weight of the B-axle, the steel bolt is sometimes partially hollow.
In view of the above, it will be apparent to those skilled in the art from this disclosure that there exists a need for an improved bicycle rear derailleur. This invention addresses this need in the art as well as other needs, which will become apparent to those skilled in the art from this disclosure.